The Habitable-zone Planet Finder Detects a Terrestrial-mass Planet Candidate Closely Orbiting Gliese 1151: The Likely Source of Coherent Low-frequency Radio Emission from an Inactive Star

TL;DR

This paper reports the detection of a terrestrial-mass exoplanet candidate orbiting Gliese 1151, which is likely the source of observed low-frequency radio emissions, demonstrating the potential of star-planet interaction studies for exoplanet detection.

Contribution

It presents the first combined radio and radial velocity evidence for a terrestrial exoplanet around an inactive star, validating star-planet interaction as a detection method.

Findings

Detection of a 2.5 Earth-mass planet candidate on a 2.02-day orbit.

Radio emission consistent with star-planet interaction models.

No flares or activity detected in TESS photometry.

Abstract

The coherent low-frequency radio emission detected by LOFAR from Gliese 1151, a quiescent M4.5 dwarf star, has radio emission properties consistent with theoretical expectations of star-planet interactions for an Earth-sized planet on a 1-5 day orbit. New near-infrared radial velocities from the Habitable-zone Planet Finder (HPF) spectrometer on the 10m Hobby-Eberly Telescope at McDonald Observatory, combined with previous velocities from HARPS-N, reveal a periodic Doppler signature consistent with an $m\sin i = 2.5 \pm 0.5 M_\oplus$ exoplanet on a 2.02-day orbit. Precise photometry from the Transiting Exoplanet Survey Satellite (TESS) shows no flares or activity signature, consistent with a quiescent M dwarf. While no planetary transit is detected in the TESS data, a weak photometric modulation is detectable in the photometry at a $\sim2$ day period. This independent detection of a candidate planet signal with the Doppler radial-velocity technique adds further weight to the claim of the first detection of star-exoplanet interactions at radio wavelengths, and helps validate this emerging technique for the detection of exoplanets.